Polyethylene Monomer: Ethylene High Density Polyethylene (HDPE) - PowerPoint PPT Presentation

Polyethylene Monomer: Ethylene  High Density Polyethylene (HDPE)  Low Density Polyethylene (LDPE)  Linear Low Density Polyethylene (LLDPE) 1

 Low Density Polyethylene (LDPE)  High Density Polyethylene (HDPE )  High degree of short and long chain  Low degrees of branching (essentially branching linear)  Density - 0.910 – 0.940 g/cm 3  Density > 0.940 g/cm 3  Lower tensile strength and increased  High tensile strength  Various catalysts (ZN, Metallocene) ductility  Free radical polymerization  Milk jugs, detergent bottles, garbage  Plastic bags and film wrap containers and water pipes Long chain branching Short chain branching Hyperbranched (HDPE) (LLDPE) (LDPE) 2

Timeline of Polyethylene  1898  Synthesized by accident while heating diazomethane (Called Poly- “ methylene ” due to repeating – CH 2 group)  1930-35  First polymerization of ethylene at Imperial Chemical Industries.  Advent of the free radical process to produce LDPE 3

Free Radical Polymerization 1. INITIATION (You need Initiators) AIBN Benzoyl Peroxide 4

Free Radical Polymerization 2. PROPAGATION High pressure is needed during the propagation step in order to bring the ethylene monomer closer to the free radicals 5

Free Radical Polymerization 3. TERMINATION (Many ways) a. COUPLING 6

Free Radical Polymerization 3. TERMINATION (Many ways) b. DISPROPORTIONATION 7

Free Radical Polymerization 3. TERMINATION (Many ways) c. CHAIN TRANSFER (Hydrogen Abstraction) 8

Free Radical Polymerization SIDE REACTIONS (Causes Branching) 9

Disadvantages 1. Uncontrolled Process • Structure, Molecular weight 2. Requires high pressure 3. Reactions are highly exothermic 4. Inefficient process (20% ethylene polymerized) 10

Timeline of Polyethylene  1898  Synthesized by accident while heating diazomethane (Called Poly- “ methylene ” due to repeating – CH 2 group)  1930-35  First polymerization of ethylene at Imperial Chemical Industries.  Advent of the free radical process to produce LDPE  1950’s  Ziegler-Natta Catalyst (Inorganic Catalyst for HDPE) 11

Zieglar-Natta Catalyst 12

Zieglar-Natta Catalyst Mechanism 13

Timeline of Polyethylene  1898  Synthesized by accident while heating diazomethane (Called Poly- “ methylene ” due to repeating – CH 2 group)  1930-35  First polymerization of ethylene at Imperial Chemical Industries.  Advent of the free radical process to produce LDPE  1950’s  Ziegler-Natta Catalyst (Inorganic Catalyst for HDPE)  1970’s  Metallocene Catalyst (Organic-Inorganic Hybrid Catalyst for HDPE) 14

Metallocene Catalyst Zirconium Sandwich The Bread is Cyclopentadiene The Filling is Zr bonded to Chlorine 15

Timeline of Polyethylene  1898  Synthesized by accident while heating diazomethane (Called Poly- “ methylene ” due to repeating – CH 2 group)  1930-35  First polymerization of ethylene at Imperial Chemical Industries.  Advent of the free radical process to produce LDPE  1950’s  Ziegler-Natta Catalyst (Inorganic Catalyst for HDPE)  1970’s  Metallocene Catalyst (Organic-Inorganic Hybrid Catalyst for HDPE)  What is next ?  Organic Routes (biological enzymatic reactions) 16

Zieglar-Natta Catalyst Mechanism 17